Existing hybrid marine drives are based around using an electric motor, attached to the back of an internal combustion engine, between the engine and a gearbox, to drive a propeller shaft of the boat. For example, with reference to FIG. 1, the internal combustion engine 10 and the electric motor/generator unit 12 are coupled via a one-way-clutch or a mechanically/electrically/hydraulically operated clutch. The electric motor/generator unit 12 is interposed between the engine 10 and a gearbox 14, which drives the propeller shaft 16. Such a system is able to turn the propeller shaft 16 using only the electric motor, a combination of the electric motor and the internal combustion engine, or only the internal combustion engine.
However, to correctly power manage an electric hybrid system in a boat, there needs to be an additional degree of freedom. Current systems do not allow the internal combustion engine to spin faster than the propeller shaft and, in twin engine installations, do not allow one engine to spin faster than the other, thus not allowing one engine to provide more power or load than the other. If this were to occur, the boat would be driven off course, favouring the side that produces more propeller shaft speed.
FIGS. 2 and 3 show traditional arrangements incorporating drive systems as shown in FIG. 1. More particularly, FIG. 2 shows a traditional single engine arrangement, and FIG. 3 shows a traditional twin engine arrangement. Each of these arrangements does not allow the internal combustion engine 10 to spin faster than the propeller shaft 16, and the twin engine arrangement shown in FIG. 3 does not allow one engine to spin faster than the other engine without the boat being driven off course.
Furthermore, each of the arrangements shown in FIG. 2 and FIG. 3 necessitates a separate generator unit 18 for powering an AC power circuit 20 of the boat. Power to the AC power circuit 20 is also provided by a house battery 22 (charged by an alternator 24), via an invertor 26. In the case of the traditional twin engine arrangement shown in FIG. 3, each of the internal combustion engines 10 is provided with a separate start battery 28.
FIGS. 4 and 5 show previously proposed hybrid marine drives, wherein each of the internal combustion engines 10 is coupled to an associated electric motor/generator unit 12 via a clutch 30. In turn, each of the electric motor/generator units 12 drives an associated gearbox 14, an output of which is coupled to drive the associated propeller shaft 16. The single engine arrangement shown in FIG. 4 and the twin engine arrangement shown in FIG. 5 both utilise a separate generator unit 18 which is driven by its own internal combustion engine. Also included is a power controller 32 which converts battery power into higher voltage to allow the electric motors 12 to drive the propeller shafts 16, and which also converts power from the electric motor/generator units 12 to charge the house battery 22. Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous hybrid marine drive arrangements.